class Base64 {
	constructor() {
		this.base64EncodeChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
		this.base64DecodeChars = new Array(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57,
			58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6,
			7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
			25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
			37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
	}
	encode(str) {
		const len = str.length;
		const base64EncodeChars = this.base64EncodeChars;
		let c1, c2, c3, i = 0,
			out = '';
		while (i < len) {
			c1 = str.charCodeAt(i++) & 0xff;
			if (i === len) {
				out += base64EncodeChars.charAt(c1 >> 2);
				out += base64EncodeChars.charAt((c1 & 0x3) << 4);
				out += '==';
				break;
			}
			c2 = str.charCodeAt(i++);
			if (i === len) {
				out += base64EncodeChars.charAt(c1 >> 2);
				out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
				out += base64EncodeChars.charAt((c2 & 0xF) << 2);
				out += '=';
				break;
			}
			c3 = str.charCodeAt(i++);
			out += base64EncodeChars.charAt(c1 >> 2);
			out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
			out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
			out += base64EncodeChars.charAt(c3 & 0x3F);
		}
		return out;
	}
	decode(str) {
		const len = str.length;
		const base64DecodeChars = this.base64DecodeChars;
		let c1, c2, c3, c4, i = 0,
			out = '';
		while (i < len) {
			do {
				c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
			} while (i < len && c1 == -1);
			if (c1 === -1) {
				break;
			}
			do {
				c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
			} while (i < len && c2 == -1);
			if (c2 === -1) {
				break;
			}
			out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
			do {
				c3 = str.charCodeAt(i++) & 0xff;
				if (c3 === 61) {
					return out;
				}
				c3 = base64DecodeChars[c3];
			} while (i < len && c3 == -1);
			if (c3 === -1) {
				break;
			}
			out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
			do {
				c4 = str.charCodeAt(i++) & 0xff;

				if (c4 === 61) {
					return out;
				}
				c4 = base64DecodeChars[c4];
			} while (i < len && c4 === -1);
			if (c4 === -1) {
				break;
			}
			out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
		}
		return out;
	}
}

module.exports = Base64;
